This application claims the priority of German patent document 199 03 386.2, filed Jan. 29, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a structure for the thermal insulation of satellites.
The necessity for insulating spacecraft against the extreme thermal influences of space is a generally recurring problem of satellite construction. The process of designing, producing, adapting and finally mounting such thermal insulation (usually by means of the so-called multi-layer insulation (MLI) technique, described below) is costly in terms of both time and expense, as explained in detail on the example of solar generators mounted on the satellite.
Stationary solar generators (whose rear-side heat radiation capacity is impaired by the satellite body) become extremely hot during phases of vertical sun irradiation (typically +100.degree. C.), but cool down significantly when in the earth's shadow. Thus, high-expenditures for interior insulation are required so that these high temperature fluctuations will not be introduced into the satellite.
In general, solar generators usually have the following mechanical construction (for example, ROSAT, CLUSTER satellites):
1. The solar cells are glued to the exterior side of a sandwich-type panel with cover layers of carbon-fiber reinforced plastic (CFK). This plastic material as well as the cellular glass have a similar coefficient of thermal expansion, thus reducing the risk of detachment of the cells during temperature fluctuations. PA1 2. A multi-layer insulation (MLI) is situated on the rear side of the sandwich-type panel. These are thin foils (typically, a thickness of 0.01 mm) which are placed above one another and are aluminum-coated on both sides by vaporizing. Mutual contact between the individual foils is minimized by means of thin plastic nets or by the structuring of the foils, so that transfer can occur only by radiation exchange between the foils, which is, however, significantly reduced by the metal coating. PA1 3. This is followed by the bearing structure of the satellite (that is, the actual satellite body), which often has an aluminum construction. In this case, suspension of the solar generator panel must either be statically defined or take place by means of a "soft" suspension which compensates the different temperature-caused deformations, in which case it must be taken into account that such suspension always has a thermal insulating effect. PA1 Reduction of the overall mass of the satellite; PA1 reduction of the design expenditures; PA1 simplification of construction and of the integration; PA1 savings as the result of fewer manual operations (MLI adaptation, etc.). PA1 Because of the elimination of the need for separate panels, the overall mass of the satellite is reduced. PA1 Since fewer components and interfaces are required compared to the known structure, design expenditures are reduced. PA1 The construction and the integration of the structure are simplified (good mechanical working, easy handling). PA1 Fewer manual operations are required, which saves costs.
In the described embodiment a front-constructed separate panel is required in addition to the actual load-bearing structure of the satellite.
Polyimides have long been used in space operations, and play an important role particularly in the field of insulation foils (for example, "Capton" foils as exterior layers of the above-described MLIs). Furthermore, they are used as open-pore foam for sound insulation on the interior of payload panelings for carrier rockets (U.S. Pat. No. 5,670,758).
It is an object of the invention to provide a structure for the thermal insulation of satellites which achieves the following goals:
These and other objects and advantages are achieved by the method and apparatus for the thermal insulation of satellites according to the invention, in which a layer of open-pore polyimide foam is applied directly to the satellite bearing structure.
Because of the good thermal insulation qualities of the polyimide foam, the temperature range of the bearing structure of the satellite disposed underneath is moderate. Therefore, a front-constructed separated panel, as used in the known structures, is not necessary. Moreover, the bearing structure may be constructed particularly as a low-cost aluminum sandwich because no critical thermal deformations occur due to the good thermal insulation properties of the polyimide foam.
The structure according to the invention has the following advantages:
The thermal insulation effect of the structure according to the invention is in the same range as that of the known structures in which MLI's are used. It also has a sufficient mechanical bearing capacity.
In addition, the structure according to the invention has no effect on the standardized solar cell mounting, as it is used in the case of the known solar generators.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.